Marketwatch reported: “Over the past two decades, there have been 846 ‘significant’ accidents from onshore gas transmission, resulting in 33 fatalities, 173 injuries and $757 million in property damage, according to the U.S. Department of Transportation.”

A firefighter stands atop an engine to survey the fire in San Bruno, CA, after a gas line explosion on Thursday, Sept. 9, 2010. (Brant Ward, San Francisco Chronicle)

In perhaps the most infamous incident, on August 19, 2000, corrosion of a 30-inch diameter natural gas pipeline caused a major explosion in Carlsbad, N.M., killing a dozen people, including four children, who were camping under a bridge that supported the pipeline over the Pecos River.
The cause of the PG&E explosion in the San Francisco middle-income suburb of San Bruno is not known. PG&E is checking reports that neighbors had reported a gas smell to the utility in recent weeks, and an engineering professor told KCBS that corrosion in a 24-inch transmission line was a possible source. (UPDATE: News sources put the size of the line at 30 inches).

A Wikipedia list of gas line accidents shows about 20 explosions that have caused fatalities in the U.S. over the last 40 years. While the gas industry says its safety record is outstanding compared to other means of transportation, industry observers told the Washington Independent that federal oversight by the Pipeline and Hazardous Materials Safety Administration is weak.